A photomask is used during the manufacture of an integrated circuit (IC) to transfer the design of each chip layer onto a semiconductor substrate. Since a photomask contains the pattern for a single layer of the chip, a set of 15 to 30 photomasks is typically used in the construction of a chip. Photomasks are reusable and typically comprise a substrate, a reflective layer, and an absorber layer.
Extreme ultraviolet (EUV) lithography is a promising new patterning technology for producing very small (i.e. −14 nm) chips. EUV lithography, like optical lithography, uses a set of photomasks which reflect EUV light to form a patterned photoresist on a semiconductor substrate.
Photomasks for EUV lithography are generally manufactured by etching the chip layer pattern into the photomask. This process has a low tolerance for error, since any defects in the photomask will be transferred to the semiconductor substrate during EUV lithography. To manufacture a photomask, a substrate (e.g., quartz) is typically etched in an etching chamber wherein a photomask can be exposed to various processing gasses and plasmas.
Within the etching chamber it is desired to achieve a uniform distribution of gas to ensure proper etching of the substrate. Uniformity of gas distribution is affected by the internal dynamics of a plasma etching chamber. Uneven gas distribution within the chamber creates unwanted variations in substrate fabrication, known as “process fingerprints.” These process fingerprints can damage device structures, leading to degraded chip performance or, in extreme cases, an unusable chip.